1. Field of the Invention
This invention generally relates to self-propelled vehicles, and more particularly, to a light-weight rigid frame wheelchair that does not utilize any weld joints but all of the structural elements are joined together only with pressure clamps.
2. Description of the Prior Art
Wheelchairs, used to transport those that are mobility impaired, have been available since the turn of the century. The first wheelchairs were bulky, heavy and extremely difficult to maneuver.
In 1932 the first tubular steel forming frame wheelchair was introduced by harry Jennings which was considerably lighter and easier to maneuver. It necessarily used folding mechanisms consisting of movable joints, linkages, etc. to connect the side frames of the chair.
Today's lifestyle is significantly more dynamic in every population segment including the disabled. This has prompted a wide market demand for a lighter, more durable, maneuverable and compact (when folded or disassembled) chair to allow for transportability in today's smaller cars. To satisfy the newly created market demand, in the late 1970s a conceptually new wheelchair with a rigid frame design was introduced.
The rigid frame wheelchair's side frames are secured to each other by rigid elements (tubes, bars, etc.) by means of welding. The absence of the folding mechanism in a rigid wheelchair provides the following advantages:
increased strength and durability (less moving parts) PA1 increased energy efficiency (folding mechanism absorbs energy needed to propel the chair) PA1 decreased weight (less parts) PA1 increased maneuverability PA1 increased stability PA1 increased comfort
Unfortunately, the existing welded rigid frame design chairs are prohibitively expensive due to high cost of manufacturing.
Examples of such wheelchairs that utilize welded joints are disclosed in U.S. Pat. Nos. 4,840,390 and 4,981,305 issued to Lockard et al. In Lockard, identical side frames are made up of a pair of generally L-shaped tubular numbers that are welded together. A sports wheelchair is disclosed in U.S. Pat. No. 4,500,102 issued to Haury et al that includes a one piece, welded tubular frame assembly. Another U.S. Pat. No. 4,721,321 issued to Haury et al discloses a similar sports wheelchair construction. Another welded wheelchair frame is disclosed in U.S. Pat. No. 4,811,964 issued to Horn for a wheelchair propelled by rowing.
A folding frame wheelchair that is movable between an upper normal sitting position and a lower reclining position that does not utilize welds is disclosed in U.S. Pat. No. 5,011,175 issued to Nicholson et al. However, such chair is a folding frame wheelchair. While it includes no welds, it is secured together by means of pivoted members or linkages that render the chair construction less stable and less secure. The chair has all the disadvantages of folding frame wheelchairs.
Also known are numerous clamping element designs for securing two or more tubular members to each other. By way of example only, reference is made to U.S. Pat. No. 4,515,497 issued to Gillemot et al for a clamping element for releasable fastening of spatially arranged, or parallel bars, tubes and similar objects; U.S. Pat. No. 4,039,263 issued to Bassler for a connector joint; U.S. Pat. No. 4,695,179 to Schnell for a fastening arrangement for a minimum of three struts along the spatial axes; U.S. Pat. No. 4,294,561 to Chapman et al for a jointing member for frame systems; U.S. Pat. Nos. 4,597,140 and 4,597,690 issued to Girard for tube clamps; U.S. Pat. No. 3,423,113 issued to Gonsalves et al for a connection for tubular members; U.S. Pat. No. 4,784,511 issued to Greene for a connector for tubular frame members; and U.S. Pat. No. 3,216,752 issued to Rifken for coupling means for building frameworks, racks, scaffolds and the like. In U.S. Pat. No. 4,702,638 issued to Zalesak, inexpensive, knock-down furniture assembled with mating, molded, plastic shells for corners and elbows is disclosed.
Notwithstanding the fact that numerous clamps have been proposed for securing tubular members to each other, the wheelchair industry has continued to rely on welded frame constructions for rigid wheelchairs. However, the welding/brazing operation proved to be inconsistent, hazardous, time consuming and expensive. It results in metal fatigue due to crystallization/oxidation, creates a heat-effected zone next to the weld which could lead to a potential safety hazard (i.e. collapse of the chair). It also requires additional operations such as polishing/grinding, electrochemical plating, etc., all of which are hazardous to both workers and environment.
All of the above processes would have to be repeated in the case of an accidental failure of the chair (i.e. weld breakage), which would entail a prohibitively high repair cost.